This invention relates to lighting systems which control the intensity of illumination such as in stage system or other lighting applications where the ability to electronically adjust the level of illumination is desired. In particular, this invention relates to controlling the intensity of light emitted from high-pressure discharge lamps.
In the past, the light intensity from high-pressure discharge lamps are generally not been adjusted. Incandescant lamp dimmers or fluorescent lamp dimmers (either with voltage feedback or with no feedback circuitry) are not satisfactory for dimming high-pressure discharge lamps. Incandescant lamp dimmers are generally not restricted to a particular fixed load but can instead be used with a varying number of lamps. Because the load current is dependent on the load which is connected, such dimmers cannot control the current and thus current feedback, if any, merely limits the maximum load current, rather than providing a regulating or stabilization function. Further, as stabilizing feedback circuits in regulated incandescent dimmers control the voltage to the load, such dimmers are not appropriate for high-pressure discharge lamps (the intensity from a high-pressure discharge lamp is not proportional to lamp voltage).
An additional problem which arises with high-pressure discharge lamps is that it is somewhat more difficult to design dimmers for more than one or two high-pressure discharge lamps, and thus a large number of dimmers will be required in most applications. Thus, for high-pressure discharge lamps, the cost, size, and weight of the dimmers is especially important.